I just did this last week and you receive an e-mail with the number and instructions on how to apply for the exam. In fact, if you don't apply right away, the PMI system will send you reminders. I had to wait a few days to get re-reimbursement approval, so I received a couple of reminders.
I believe that you will receive your member number almost immediately. But no matter how long it actually takes - the sooner you join the sooner you have it.
I would like to join PMI and take advantage of the discount on the exam. Does anyone know how long it takes to receive the membership ID so I can apply for the PMP exam and get the membership rate?
Training for Project Management Professional (PMP)®, PMI Agile Certified Practitioner (PMI-ACP)®, and Certified Associate in Project Management (CAPM)®